JP7523394B2 - Wheel Loader - Google Patents

Description

The present invention relates to a wheel loader having a bucket.

As background art in this technical field, for example, Patent Document 1 describes a wheel loader configured such that when a switch is operated for the purpose of absorbing pressure fluctuations in the bottom chamber of the boom cylinder, the controller sends a signal so that the ride control valve communicates between the accumulator and the bottom chamber of the boom cylinder.

JP 2007-186942 A

The condition of the road surface on which the wheel loader travels varies depending on the work site, and some roads are rough with a series of steps on the road surface. When there are a series of steps on the road surface, the accumulator cannot fully absorb the pressure fluctuations in the bottom chamber of the lift arm cylinder (boom cylinder), and as a result, there is a possibility that the soil and sand in the bucket will spill out due to vibration. In Patent Document 1, the configuration is limited to absorbing vibration using the accumulator, and when the wheel loader travels on a rough road with a series of steps, the vibrations are amplified and there is a possibility that the vibrations cannot be absorbed. If the wheel loader travels in a state where it cannot absorb vibrations, the soil and sand that needs to be moved will spill out of the bucket.

The present invention aims to provide a wheel loader that prevents soil and sand from spilling out of the bucket without the need to adjust vehicle speed, even when traveling on rough roads.

In order to achieve the above object, a representative embodiment of the present invention is a wheel loader including a vehicle body having front and rear wheels, a bucket provided at the front of the vehicle body, a lift arm that holds the bucket, a lift arm cylinder that drives the lift arm, an engine that is the drive source of the vehicle body, and a control device that controls the engine speed. The wheel loader is also equipped with an angle sensor that detects the angle of the lift arm, an accumulator that is connected to the hydraulic chamber of the lift arm cylinder and allows pressurized oil to flow in and out of the hydraulic chamber, and a pressure sensor that detects the pressure of the accumulator, and is characterized in that when the angle of the lift arm detected by the angle sensor satisfies a deceleration control condition for decelerating the engine speed, the control device decelerates the engine speed based on the pressure of the accumulator detected by the pressure sensor.

The present invention provides a wheel loader that is less likely to spill soil or sand from the bucket. Moreover, the present invention does not require adjustment of vehicle speed even when traveling on rough roads. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiment.

FIG. 1 is a side view of a wheel loader according to an embodiment of the present invention. 1 is a perspective view of a wheel loader according to an embodiment of the present invention. FIG. FIG. 2 is a diagram showing a drive system configuration of the wheel loader. FIG. 2 is a diagram showing a system configuration of a traveling vibration suppression hydraulic circuit. 11A and 11B are diagrams showing pressure fluctuations in a bottom chamber of a lift arm cylinder and changes in the cylinder length of the lift arm cylinder when a wheel loader goes over a step. FIG. 11 is a diagram showing pressure fluctuations in a bottom chamber of a lift arm cylinder when a wheel loader goes over successive steps at the same vehicle speed. FIG. 11 is a diagram showing a comparison of pressure fluctuations in the bottom chamber of the lift arm cylinder when the wheel loader goes over a step at different vehicle speeds. 11 is a diagram showing pressure fluctuations in a bottom chamber of a lift arm cylinder when a wheel loader first goes over a step, then decelerates and goes over the next step. FIG. FIG. 2 is a block diagram illustrating a hardware configuration of a main controller. FIG. 2 is a block diagram showing the electrical configuration of the wheel loader. FIG. 2 is a functional block diagram of a main controller. 5 is a flowchart showing a processing procedure of a deceleration control determination unit. 10 is a flowchart showing a processing procedure of a deceleration gain calculation unit. FIG. 4 is a map diagram showing the relationship between the reference pressure and the deceleration gain. FIG. 13 illustrates the change in reference pressure over time. 5 is a flowchart showing a processing procedure of a command rotation speed calculation unit. FIG. 4 is a map diagram showing the relationship between the depression amount of the accelerator pedal and the required engine speed.

Below, an embodiment of a wheel loader according to the present invention will be described with reference to the drawings.

Figure 1A is a side view of a wheel loader according to an embodiment of the present invention, and Figure 1B is a perspective view of a wheel loader according to an embodiment of the present invention.

As shown in Figures 1A and 1B, the wheel loader 1 is composed of a front frame (vehicle body) 6 having a lift arm 11, a bucket 3, a pair of front wheels 5, etc., and a rear frame (vehicle body) 8 having a driver's cab 4, an engine room 20, a pair of rear wheels 7, etc. An engine 100 is mounted in the engine room 20, and a counterweight 21 is attached to the rear of the rear frame 8. The front frame 6 and the rear frame 8 are rotatably connected to each other by a center pin 9, and the front frame 6 bends left and right relative to the rear frame 8 due to the extension and contraction of the steering cylinder 10. In the following description, the front wheels 5 and rear wheels 7 may be collectively referred to as "wheels 5, 7".

The lift arm 11 rotates vertically (elevates or lowers) when driven by a pair of lift arm cylinders 12, and the bucket 3 rotates vertically (crowds or dumps) when driven by a bucket cylinder 16. A link mechanism including a bell crank 15 and a push rod 14 is provided between the bucket cylinder 16 and the bucket 3, and the bucket cylinder 16 rotates the bucket 3 via this link mechanism. The lift arm 11, bucket 3, pair of lift arm cylinders 12, bucket cylinder 16, bell crank 15, push rod 14, etc. constitute the work machine 2.

A lift arm angle sensor (angle sensor) 18 is attached to the connection between the lift arm 11 and the front frame 6, and this lift arm angle sensor 18 detects the rotation angle of the lift arm 11. In addition, a bucket angle sensor 19 is attached to a specified position of the bell crank 15, which detects the angle of the bucket 3 relative to the lift arm 11.

The cab 4 mounted on the front of the rear frame 8 is equipped with a driver's seat where the operator sits, a steering wheel 117 that controls the steering angle of the wheel loader 1, a key switch that starts and stops the wheel loader 1, a monitor that displays information to the operator, and a main controller (control device) 121 that controls the overall operation of the wheel loader 1.

Figure 1A shows the posture of the wheel loader 1 during transport operations. During transport operations, the lift arm 11 is raised to a height where the bucket 3 does not block the view of the operator in front, so that the bucket 3 that has scooped up soil and sand does not come into contact with the ground while traveling.

Figure 2 is a diagram showing the drive system configuration of the wheel loader 1. As shown in Figure 2, the output shaft 100a of the engine 100 is directly connected to a torque converter 101, a hydraulic pump 102, and a brake pump 103. The rotation speed of the output shaft 100a of the engine 100 is controlled by an electrical signal 105 from an engine controller (control device) 104, and the engine controller 104 outputs the electrical signal 105 based on a rotation speed command 127 from a main controller 121. The main controller 121 outputs the rotation speed command 127 based on the amount of depression of the accelerator pedal 106.

The output shaft of the torque converter 101 is connected to the drive shaft 108 via the transmission 107, and the driving force of the engine 100 is transmitted to the wheels 5 and 7 via the torque converter 101, the transmission 107, and the drive shaft 108. As a result, the wheels 5 and 7 rotate.

The torque converter 101 is a fluid clutch composed of an impeller, a turbine, and a stator. The driving force transmitted from the torque converter 101 to the transmission 107 increases as the rotation speed of the output shaft 100a of the engine 100 increases relative to the output rotation speed of the torque converter 101. By increasing the rotation speed of the engine 100 by the depression amount of the accelerator pedal 106, the driving force output by the torque converter 101 increases. When there is no difference between the output rotation speed of the torque converter 101 and the rotation speed of the output shaft 100a of the engine 100, the driving force output by the torque converter 101 becomes 0.

When traveling on flat ground where the traveling resistance acting on the wheels 5, 7 is constant, if the rotation speed of the output shaft 100a of the engine 100 is constant, the traveling speed will also be constant. When the rotation speed of the output shaft 100a of the engine 100 is increased, the wheel loader 1 accelerates, and when the rotation speed of the output shaft 100a of the engine 100 is decreased, the wheel loader 1 decelerates.

The transmission 107 cuts off the connection between the output of the torque converter 101 and the drive shaft 108 based on an electrical signal 110 from the transmission controller 109, thereby reducing the driving force to the wheels 5 and 7, or reversing the direction of rotation to change the direction of the driving force.

Specifically, the transmission 107 controls the combination of multiple gears so that the gear ratio corresponds to one of the speed stages, for example, 1 to 4, during forward or reverse driving. As a result, the torque, rotation speed, and rotation direction of the output shaft of the torque converter 101 are transmitted to the wheels 5 and 7 according to the set speed stage.

The electrical signal 110 from the transmission controller 109 is output to cut off the connection when the operator's forward/reverse command switch 111 is in neutral and when the brake pedal 112 is depressed to a certain degree or greater.

The transmission 107 is also fitted with a vehicle speed sensor (not shown) that measures the rotation speed of the drive shaft 108, and the transmission controller 109 measures the vehicle speed of the wheel loader 1 based on the vehicle speed sensor. Note that instead of using the vehicle speed sensor, the vehicle speed of the wheel loader 1 may be measured by directly detecting the rotation speed of the wheels 5, 7.

The hydraulic pump 102 outputs a constant flow rate of pressurized oil each time the output shaft 100a of the engine 100 rotates once. In this embodiment, the hydraulic pump 102 is a variable displacement hydraulic pump of a swash plate type or a swash axis type in which the displacement volume is controlled according to the tilt angle, but a fixed displacement hydraulic pump may also be used.

The pressurized oil output from the hydraulic pump 102 is supplied to the lift arm cylinder 12 and the bucket cylinder 16 via the work machine control hydraulic circuit 113, causing the lift arm cylinder 12 and the bucket cylinder 16 to extend and retract.

The amount of pressurized oil output from the hydraulic pump 102 increases as the rotation speed of the output shaft 100a of the engine 100 increases, so when the rotation speed of the engine 100 is increased by depressing the accelerator pedal 106, the extension and retraction speed of the lift arm cylinder 12 and bucket cylinder 16 increases.

When the operator operates the lift lever 114, the work machine control hydraulic circuit 113 cuts off the connection between the output of the hydraulic pump 102 and the lift arm cylinder 12 to stop the operation of the lift arm 11, reverse the extension/retraction direction, and switch the up/down movement of the lift arm 11.

When the operator operates the bucket lever 115, the work machine control hydraulic circuit 113 cuts off the connection between the output of the hydraulic pump 102 and the bucket cylinder 16 to stop the operation of the bucket 3, reverse the extension direction, and switch the forward/backward movement of the angle of the bucket 3.

The pressurized oil output from the hydraulic pump 102 is connected to the left and right steering cylinders 10 via the steering control hydraulic circuit 116, and extends and retracts the left and right steering cylinders 10.

When the operator rotates the steering wheel 117 to the right, the steering control hydraulic circuit 116 connects the pressurized oil output from the hydraulic pump 102 to the direction in which the right steering cylinder 10R contracts and the direction in which the left steering cylinder 10L extends, turning the wheel loader 1 to the right, and when the operator rotates the steering wheel 117 to the left, the steering control hydraulic circuit 116 connects the pressurized oil output from the hydraulic pump 102 to the direction in which the right steering cylinder 10R extends and the direction in which the left steering cylinder 10L contracts, turning the wheel loader 1 to the left.

The pressurized oil output from the brake pump 103 is stored in the accumulator 118, and the pressurized oil stored in the accumulator 118 controls the braking force of the wheels 5 and 7 via the brake control hydraulic circuit 119.

The brake control hydraulic circuit 119 adjusts the control pressure according to the amount of depression of the brake pedal 112 by the operator.

Figure 3 is a diagram showing the system configuration of the traveling vibration suppression hydraulic circuit 123 shown in Figure 2. As shown in Figure 3, the control valve solenoid valve 201 is driven by an excitation signal (electrical signal) 305 from the main controller 121. When in an excited state, the control valve solenoid valve 201 switches to position 201a, and the pressure of the pilot hydraulic source 202 acts on the switching valve 203. Then, the switching valve 203 switches to the communicating position 203a. On the other hand, when in a non-excited state, the control valve solenoid valve 201 switches to position 201b, and the switching valve 203 switches to the non-communicating position 203b.

When the switching valve 203 is in the communication position 203a, the bottom chamber (hydraulic chamber) 12b of the lift arm cylinder 12 communicates with the accumulator 124, and pressure oil flows in and out between them. Also, the rod chamber 12c of the lift arm cylinder 12 communicates with the tank 204, and pressure oil in the rod chamber 12c is led to the tank 204. On the other hand, when the switching valve 203 is in the non-communication position 203b, communication between the accumulator 124 and the bottom chamber 12b of the lift arm cylinder 12 is cut off, and communication between the rod chamber 12c of the lift arm cylinder 12 and the tank 204 is cut off.

The accumulator pressure sensor 205 measures the pressure of the accumulator 124 and outputs a pressure signal 206 to the main controller 121.

When the traveling vibration suppression control changeover switch 126 is ON, the detection value of the lift arm angle sensor 18 is a predetermined value, and the vehicle speed is equal to or higher than a certain speed, the main controller 121 outputs an excitation signal 305 to the control valve solenoid valve 201, and does not excite in other cases (details will be described later).

Although not shown, the main controller 121, engine controller 104, and transmission controller 109 are all connected via a communication network.

Figure 4 shows the pressure fluctuation in the bottom chamber 12b of the lift arm cylinder 12 and the change in the cylinder length of the lift arm cylinder 12 when the wheel loader 1 goes over a step. In Figure 4, the upper part shows the pressure in the bottom chamber 12b of the lift arm cylinder 12, and the lower part shows the change in the cylinder length of the lift arm cylinder 12.

When the switching valve 203 is in the communication position 203a, the accumulator 124 and the bottom chamber 12b of the lift arm cylinder 12 are in communication with each other, so the pressure fluctuation of the accumulator 124 is equal to the pressure fluctuation of the bottom chamber 12b of the lift arm cylinder 12. Therefore, the accumulator pressure detected by the accumulator pressure sensor 205 can be regarded as the pressure P of the bottom chamber 12b of the lift arm cylinder 12.

When the front wheels 5 of the wheel loader 1 run over a step, as shown in section 1a, the pressure P in the bottom chamber 12b of the lift arm cylinder 12 rises. The accumulator 124 absorbs the rise in pressure P in the bottom chamber 12b of the lift arm cylinder 12, causing the cylinder length L of the lift arm cylinder 12 to decrease.

In section 1b, the pressurized oil stored in the accumulator 124 is guided to the bottom chamber 12b of the lift arm cylinder 12, causing the cylinder length L of the lift arm cylinder 12 to extend.

When the front wheels 5 of the wheel loader 1 climb over the step and land, the pressure P in the bottom chamber 12b of the lift arm cylinder 12 rises, as shown in section 1c. The accumulator 124 absorbs the rise in pressure P in the bottom chamber 12b of the lift arm cylinder 12, causing the cylinder length L of the lift arm cylinder 12 to decrease. After that, the cylinder length L of the lift arm cylinder 12 expands and contracts, while the fluctuation in pressure P in the accumulator 124 decays.

In this way, the accumulator 124 absorbs the pressure fluctuations that occur in the bottom chamber 12b of the lift arm cylinder 12, mitigating the impact that acts on the bucket 3 connected to the tip of the lift arm 11, and preventing soil and sand from spilling out of the bucket 3.

Next, we will explain the case where there are successive steps. Figure 5 is a diagram showing the pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 when the wheel loader 1 goes over successive steps at the same vehicle speed. Note that in Figure 5, sections 1a to 1c show the state where the front wheels 5 of the wheel loader 1 have gone over the first step, and are the same as sections 1a to 1c in Figure 4.

In section 2a, the front wheels 5 go over the first step, and then go over the second step before the pressure fluctuation in the bottom chamber 12b of the lift arm cylinder 12 has finished damping.

As shown in Figure 5, in section 2a, the pressure fluctuation in the bottom chamber 12b of the lift arm cylinder 12 is amplified, and the impact on the bucket 3 is also amplified, causing soil and sand to spill out of the bucket 3.

Figure 6 is a diagram showing a comparison of pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 when the wheel loader 1 goes over a step at different vehicle speeds. In Figure 6, sections 1a to 1c show a state in which the front wheels 5 go over a step at the same vehicle speed as in Figure 4, while sections 3a to 3c show a state in which the front wheels 5 go over a step at a slower speed than sections 1a to 1c. As shown in sections 3a to 3c in Figure 6, by reducing the vehicle speed of the wheel loader 1, the impact that the front wheels 5 receive from the ground is weakened, and the pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 are reduced.

Figure 7 shows the pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 when the wheel loader 1 first goes over a step, then decelerates to go over the next step. In section 4a of Figure 7, the pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 are amplified, but because the second step is passed over at a low speed, the pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 are suppressed compared to section 2a of Figure 5. As a result, the impact on the bucket 3 is also weakened, preventing soil and sand from spilling out of the bucket 3.

As such, in order to prevent soil and sand from spilling out of the bucket 3 when the wheel loader 1 overcomes successive steps, it is important to suppress the amplification of pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12.

Figure 8 is a block diagram showing a schematic hardware configuration of the main controller 121. As shown in Figure 8, the main controller 121 is composed of hardware including a CPU (Central Processing Unit) 121A that performs various calculations to control the overall operation of the vehicle body, a storage device such as a ROM (Read Only Memory) 121B that stores programs for the CPU 121A to execute the calculations, a RAM (Random Access Memory) 121C that serves as a working area when the CPU 121A executes the programs, and an input/output interface 121D that inputs and outputs various information and signals between the CPU 121A and external devices.

In such a hardware configuration, a program stored in ROM 121B is read into RAM 121C and operates under the control of CPU 121A, whereby the program (software) and hardware work together to form a functional block that realizes the functions of main controller 121, which will be described later.

The engine controller 104 and the transmission controller 109 are configured in the same way as the main controller 121.

Figure 9 is a block diagram showing the electrical configuration of the wheel loader 1. As shown in Figure 9, the main controller 121 receives vehicle speed information 301 from the transmission controller 109, ON information 302 from the travel vibration suppression control changeover switch 126, angle information 303 from the lift arm angle sensor 18, pressure signal 206 from the accumulator pressure sensor 205, and depression amount 304 of the accelerator pedal 106, and outputs a rotation speed command 127 to the engine controller 104 and an excitation signal 305 to the control valve solenoid valve 201.

Figure 10 is a functional block diagram of the main controller 121. As shown in Figure 10, the traveling vibration suppression determination unit 401 sets an excitation signal 305 to excite the control valve solenoid valve 201 of the traveling vibration suppression hydraulic circuit 123 based on vehicle speed information 301 of the wheel loader 1, ON information 302 of the traveling vibration suppression control changeover switch 126, and angle information 303 of the lift arm 11.

Specifically, when the wheel loader 1 is traveling at a predetermined speed, the traveling vibration suppression control changeover switch 126 is ON, and the lift arm 11 is within a predetermined angle range (i.e., when the bucket 3 is in a "transport posture" in which it is elevated to a certain degree above the ground), the traveling vibration suppression determination unit 401 sets the excitation signal 305. Here, the "transport posture" refers to a posture in which the bucket 3 is held by the lift arm 11 at a position slightly higher than the ground with soil or the like contained in the bucket 3; for example, the posture shown in FIG. 1A is the transport posture in this embodiment.

In this embodiment, the excitation signal 305 is set to excite the control valve solenoid valve 201 of the traveling vibration suppression hydraulic circuit 123 based on the vehicle speed information 301 of the wheel loader 1, the ON information 302 of the traveling vibration suppression control changeover switch 126, and the angle information 303 of the lift arm 11. However, it is sufficient to output the excitation signal 305 based on at least the angle information 303 of the lift arm 11. In addition, in situations where the vehicle speed is low, such as in dump loading work or excavation work, if the traveling vibration suppression control is activated, the vehicle body may become unstable, which may cause problems in dump loading work, excavation work, etc. Therefore, it is preferable that the traveling vibration suppression judgment unit 401 constantly monitors the vehicle speed information 301, and when the vehicle speed falls below a predetermined vehicle speed corresponding to dump loading work, excavation work, etc., the traveling vibration suppression judgment unit 401 does not execute this control to automatically reduce the engine speed in order to cancel the traveling vibration suppression control.

The deceleration control determination unit 402 sets the deceleration control determination signal 403 and the differential pressure 404 described below based on the excitation signal 305 and the pressure signal 206 of the accumulator 124.

Figure 11 is a flowchart showing the processing procedure of the deceleration control determination unit 402. Note that the processing shown in Figure 11 is repeated every predetermined time (e.g., 10 milliseconds).

As shown in FIG. 11, when the excitation signal 305 is OFF in S101, i.e., when the control valve solenoid valve 201 is de-excited (S101/No), the deceleration control determination unit 402 sets the reference pressure to the value of the pressure signal 206 of the accumulator 124 (detected pressure) (S108), sets the differential pressure 404 to 0 (S109), and sets the deceleration control determination signal 403 (deceleration control) to OFF (S110). In other words, deceleration control of the engine speed is not performed (the vehicle speed is not decelerated).

On the other hand, if the excitation signal 305 is ON in S101, the deceleration control determination unit 402 sets the differential pressure 404 to a value obtained by subtracting the reference pressure (previous value) from the value of the pressure signal 206 (detected pressure) (S102), and if the differential pressure 404 is greater than the set pressure in S103 (S103/Yes), it sets the timer to 0 (S104) and sets the deceleration control determination signal 403 to ON (S105). In other words, it performs deceleration control of the engine speed (slows down the vehicle speed).

Here, S103 is a process for determining whether or not there is a possibility that soil or sand will spill out of the bucket 3, or in other words, a process for determining whether or not to perform control to decelerate the engine speed. In other words, if the determination in S103 indicates that there is a possibility that soil or sand will spill out of the bucket 3, the engine speed is decelerated, and if not, the engine speed is not decelerated. Therefore, the set value in S103 is determined based on the difference in pressure (differential pressure) in the bottom chamber 12b of the lift arm cylinder 12 at which soil or sand can be deemed to spill out of the bucket 3 when the wheel loader 1 overcomes a step.

If the pressure difference 404 is equal to or less than the set value in S103 (S103/No), the deceleration control determination unit 402 sets the timer to a value obtained by adding 1 to the timer (previous value) (S106), and if the timer is less than the set time (S107/Yes), the deceleration control determination signal 403 is set to ON (S105). In other words, deceleration control of the engine speed is performed (the vehicle speed is decelerated).

On the other hand, if the timer is equal to or greater than the set time (S107/No), the deceleration control determination unit 402 sets the deceleration control determination signal 403 to OFF (S110). In other words, the engine speed is not decelerated (the vehicle speed is not decelerated).

The reason for setting the set time in S107 is that if the deceleration control is immediately turned OFF (S110) when the pressure difference 404 is equal to or lower than the set pressure in S103, there is a possibility that the wheel loader 1 will hunt. In other words, by performing the processes in S106 and S107, hunting of the wheel loader 1 is prevented.

Furthermore, if the set time is made longer, the vehicle speed will slow down, which may result in poor work efficiency, while if the set time is too short, soil and sand may spill out of the bucket 3. Therefore, in this embodiment, the set time is set to the time (e.g., 1 second) from when the front wheels 5 go over the step (specific position) until the rear wheels 7 go over the step. In other words, the set time is determined based on the vehicle speed and the wheelbase (the distance between the front wheels 5 and the rear wheels 7).

Next, the deceleration gain calculation unit 405 in FIG. 10 sets the deceleration gain 406 based on the input of the deceleration control determination signal 403 and the differential pressure 404.

Figure 12 is a flowchart showing the processing procedure of the deceleration gain calculation unit 405. Note that the processing shown in Figure 12 is repeated every predetermined time (e.g., 10 milliseconds).

As shown in FIG. 12, when the deceleration control determination signal 403 is OFF (S201/No), the deceleration gain calculation unit 405 sets the reference pressure to 0 (S206) and sets the deceleration gain 406 to 1 (S207). In other words, the vehicle speed corresponds to the depression amount 304 of the accelerator pedal 106.

In S201, if the deceleration control determination signal 403 is ON (S201/Yes), the deceleration gain calculation unit 405 compares the differential pressure 404 with the reference pressure (previous value) (S202), and if the differential pressure 404 is equal to or less than the reference pressure (previous value) (S202/No), the reference pressure is set to the reference value (previous value) (S205), and the deceleration gain 406 is set to the deceleration gain (map value) obtained by referring to the map (Figure 13) (S204).

Figure 13 is a map diagram showing the relationship between the reference pressure and the deceleration gain. As shown in Figure 13, map data with characteristics in which the deceleration gain decreases as the reference pressure increases is stored in ROM 121B. As a result, the deceleration gain decreases as the differential pressure 404 increases, and the engine speed is decelerated. For example, when the reference pressure is Pr1, the deceleration gain calculation unit 405 obtains the deceleration gain G1 (0 < G1 < 1) corresponding to the reference pressure Pr1 from the map data shown in Figure 13.

On the other hand, in S202 of FIG. 12, if the differential pressure 404 is greater than the reference pressure (previous value) (S202/Yes), the deceleration gain calculation unit 405 sets the differential pressure 404 as the reference pressure (S203), and sets the deceleration gain 406 to the deceleration gain (map value) obtained by referring to the map (FIG. 13) (S204).

In this manner, in this embodiment, when the differential pressure 404 is greater than the reference pressure (previous value), the reference pressure is set to the differential pressure (S203), and the deceleration gain (-) is increased. On the other hand, when the differential pressure 404 is equal to or less than the previous reference pressure, the reference pressure is set to the reference pressure (previous value) (S205), and the previous deceleration gain is maintained.

This will be explained in detail with reference to FIG. 14. FIG. 14 is a diagram showing the change in the reference pressure over time. As shown in FIG. 14, at time t1 when the deceleration control is turned ON, the reference pressure rises to Pr1, and the reference pressure gradually rises as time passes from time t1 to time t2. As the reference pressure rises, the deceleration gain increases (the engine speed decelerates). When the differential pressure 404 falls below the reference pressure (previous value) at time t2, the differential pressure 404 (dash line) falls, but the reference pressure is maintained at the previous value Pr2. Thus, the deceleration gain corresponding to the previous value Pr2 is maintained. Then, at time t3 when the deceleration control is turned OFF, the reference pressure becomes zero. In this way, the deceleration gain gradually increases from time t1 to time t2, and a constant deceleration gain (constant engine speed) is maintained from time t2 to time t3.

The command rotation speed calculation unit 407 shown in FIG. 10 sets the rotation speed command 127 based on the input of the deceleration gain 406 and the depression amount 304 of the accelerator pedal 106.

Figure 15 is a flowchart showing the processing procedure of the command speed calculation unit 407. The processing shown in Figure 15 is repeated every predetermined time (e.g., 10 milliseconds). As shown in Figure 15, the command speed calculation unit 407 sets the requested engine speed to the requested engine speed (map value) obtained by referring to the map shown in Figure 14 (S301).

Figure 16 is a map diagram showing the relationship between the depression amount 304 of the accelerator pedal 106 and the required engine speed (rpm). As shown in Figure 16, map data with a characteristic that the greater the depression amount 304, the greater the required engine speed is stored in ROM 121B. As a result, the more the accelerator pedal 106 is depressed, the greater the vehicle speed becomes. For example, when the depression amount 304 is V1, the command speed calculation unit 407 obtains the required engine speed N1 corresponding to the depression amount V1 from the map data shown in Figure 16.

Next, the command speed calculation unit 407 sets the engine target speed to a value obtained by multiplying the engine request speed by the deceleration gain (406) (S302). The command speed calculation unit 407 compares the engine target speed with a preset minimum engine speed (S303), and if the engine target speed is equal to or lower than the minimum engine speed in S303 (S303/No), it sets the speed command 127 to the minimum engine speed (S305). If the engine target speed is higher than the minimum engine speed in S303 (S303/Yes), it sets the engine target speed to the speed command 127. Here, the minimum engine speed is, for example, the engine speed during idling.

As described above, according to this embodiment, when the angle information 303 of the lift arm 11 satisfies the deceleration control condition of the engine 100, the main controller 121 is configured to decelerate the rotation speed of the engine 100 based on the pressure signal 206 of the accumulator 124. This makes it possible to suppress the vehicle speed when the wheel loader 1 overcomes successive steps, thereby preventing soil and sand from spilling out of the bucket 3. More specifically, by slowing down the vehicle speed, pressure fluctuations in the bottom chamber 12b of the lift arm cylinder 12 are suppressed, stabilizing the posture of the bucket 3. As a result, soil and sand are less likely to spill out of the bucket 3.

In addition, after the pressure difference in the accumulator 124 falls below the set pressure (S103/No), when the set time has elapsed (S107/NO), the deceleration control of the engine 100 ends (S110), preventing hunting of the wheel loader 1. Here, the set time is preset based on the vehicle speed of the wheel loader 1 and the distance between the front wheels 5 and rear wheels 7, so that deceleration control of the engine 100 can be reliably performed from the time when the front wheels 5 go over the step until the rear wheels 7 go over the step.

In addition, the engine speed is slowed down as the pressure difference 404 in the accumulator 124 increases (see FIG. 13), which further prevents soil and sand from spilling out of the bucket 3.

In addition, if the currently acquired differential pressure 404 of the accumulator 124 is greater than the previously acquired differential pressure, the engine speed is slowed down as the differential pressure 404 increases, and if the currently acquired differential pressure 404 is equal to or less than the previously acquired differential pressure 404, the engine speed corresponding to the previously acquired differential pressure 404 is maintained (see FIG. 14), which further prevents soil and sand from spilling out of the bucket 3.

In this way, according to this embodiment, when scooping up soil and sand into the bucket 3 for transport, even when traveling on a road surface with successive steps, the operator can prevent the soil and sand from spilling out of the bucket 3 without fine adjustments to the vehicle speed. This makes it easier to operate the transport work, improving the work efficiency of inexperienced operators.

The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. All technical matters included in the technical ideas described in the claims are the subject of the present invention. The above-described embodiment shows a preferred example, but a person skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the attached claims.

For example, if the present invention is applied to an unmanned wheel loader that performs transport work remotely without an operator on board, it is possible to prevent soil and sand in the bucket from spilling out when the wheel loader travels on a road surface with continuous unevenness. In other words, the present invention is also suitable for unmanned wheel loaders.

In the above embodiment, the driving force of the engine 100 is transmitted to the wheels 5, 7 via the torque converter 101 and the transmission 107, but the present invention can also be applied to a so-called HST (Hydro Static Transmission) type wheel loader.

1 Wheel loader 2 Work machine 3 Bucket 5 Front wheel 6 Front frame (vehicle body)
7 Rear wheel 8 Rear frame (body)
11 Lift arm 12 Lift arm cylinder 12b Bottom chamber (hydraulic chamber)
16 Bucket cylinder 18 Lift arm angle sensor (angle sensor)
100 Engine 101 Torque converter 104 Engine controller (control device)
107 Transmission 109 Transmission controller 121 Main controller (control device)
124 Accumulator 126 Travel vibration suppression control changeover switch 205 Accumulator pressure sensor (pressure sensor)

Claims (5)

A wheel loader comprising a vehicle body to which front and rear wheels are attached, a bucket provided at the front of the vehicle body, a lift arm that holds the bucket, a lift arm cylinder that drives the lift arm, an engine that is a drive source for the vehicle body, and a control device that controls the rotation speed of the engine,
an angle sensor for detecting an angle of the lift arm;
an accumulator connected to a hydraulic chamber of the lift arm cylinder and capable of allowing pressurized oil to flow in and out of the hydraulic chamber;
a pressure sensor that detects the pressure of the accumulator;
The control device includes:
and when the angle of the lift arm detected by the angle sensor satisfies a deceleration control condition for decelerating a rotation speed of the engine, the rotation speed of the engine is decelerated based on the pressure of the accumulator detected by the pressure sensor. The wheel loader according to claim 1,
The control device includes:
Calculating a differential pressure between the previous pressure of the accumulator detected by the pressure sensor and the current pressure of the accumulator detected by the pressure sensor;
when the pressure difference exceeds a set pressure, the engine starts to reduce its rotation speed, and when the pressure difference falls below the set pressure and a set time has elapsed, the engine stops reducing its rotation speed. The wheel loader according to claim 2,
A wheel loader, wherein the set time is determined in advance based on a vehicle speed of the wheel loader and a distance between the front wheels and the rear wheels. The wheel loader according to claim 1,
The control device includes:
a differential pressure between the previous pressure in the accumulator detected by the pressure sensor and the current pressure in the accumulator detected by the pressure sensor is calculated, and the larger the differential pressure becomes, the more the engine rotation speed is reduced. The wheel loader according to claim 4,
The control device includes:
when the currently acquired differential pressure is greater than the previously acquired differential pressure, the engine speed is reduced as the differential pressure increases, and when the currently acquired differential pressure is equal to or less than the previously acquired differential pressure, the engine speed corresponding to the previously acquired differential pressure is maintained.

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